Starting off as a wickedly seductive comedy about a naive youth and his unusually attentive tutor, only to take on increasingly insidious dimensions, “Private Lessons” more than confirms the rising talent of 33-year-old Belgian writer-director Joachim Lafosse. Lighter in tone and subject matter than his 2006 dysfunctional-family drama “Private Property,” but no less incisive in its examination of toxic relational dynamics and the damage that can occur in the absence of boundaries, this is a sly, superbly knowing entertainment that looks set to earn high critical marks and admission to offshore arthouses. Local release is set for Sept. 17.

Pic never spells out exactly how Jonas fell in with this trio, making their easy rapport all the more vaguely unsettling. With his divorced, hands-off parents both out of the picture, Jonas takes up residence at Pierre’s pad, where the wealthy, sophisticated bachelor decides to help him with his studies.

Tension and comedy escalate with breathtaking assurance in the pic’s expertly modulated midsection, as Pierre, Didier and Nathalie delight in every opportunity to broaden Jonas’ horizons, not all of which turn out to be exclusively academic. Nathalie and Didier go to envelope-pushing extremes to instruct Jonas how to pleasure his cute g.f., Delphine (Pauline Etienne, very good) — who, tellingly, prefers Jonas’ awkward fumblings to his later attempts to impress her with his technique.

But Jonas receives his most significant “Private Lessons” from Pierre, who repeatedly drills him in matters of calculus, Camus and, eventually, carnal knowledge. Literate screenplay (by Lafosse and Francois Pirot) really shows its teeth in the duo’s extended dialogues, as Pierre fills Jonas’ head with relativistic ideas about the fluidity of sexual orientation and the importance of not just healthy experience, but healthy experimentation.

Pic’s strength lies in its ability to extract wit, humor and a certain lusty appeal from Pierre’s worldview — even as it recognizes how poisonous said worldview can be, and how easily authority, left unchecked, can lead to abuse.

Thesps are all deliciously game, with top honors going to Bloquet as the corruptible, rosy-cheeked Jonas and Zaccai as the intimidating tutor whose ministrations can quickly turn manipulative.

Technically, pic is a work of modest precision. Reteaming with “Private Property” d.p. Hichame Alaouie and editor Sophie Vercruysse, Lafosse replicates that film’s rhythm of long, focused takes with no cuts within scenes. Widescreen lensing (a first for the helmer) and carefully worked-out camera movements easily accommodate the four central characters within the frame, particularly in their many back-and-forth conversations at the dinner table.